In many types of processes, undesirable solids are present in fluid streams. Production of sand with crude oil, waste water treatment and fermentation processes are examples of such processes. These solids can separate from the fluid when the fluids pass through containment devices which have low fluid velocities. When fluid streams which contain solids enter a low velocity flow regime, solids will settle at a rate according to, for example, Stokes law. This usually occurs in a holding tank or vessel. Accumulation of solids in such tanks and vessels may eventually require equipment shutdowns to physically remove accumulated solids. Additionally, accumulated solids decrease the volume available for fluid residence time.
Apparatuses are available which provide means to remove settled solids from fluid containment devices. These apparatuses typically comprise an inverted pan, called sand pans, centrally located over the lower surface of the fluid containment devices. Teeth are typically cut in the sides of the inverted pan to provide communication into the volume inside the pan from along the bottom of the vessel. A slurry blowdown removes slurry from the volume within the sand pan. Nozzles capable of directing a flushing fluid flow along the bottom of the vessel toward the pan are also generally provided. Flushing fluid is jetted from the nozzles along the bottom surfaces of the vessel to fluidize settled solids, and then fluids are removed via the slurry blowdown from inside the sand pan. These facilities are used intermittently to remove solids from the vessel in the form of a slurry. This arrangement is useful in removing settled solids from fluid containing devices, but eventually, fluid flowpaths will plug and the fluid containment device will require removal from service for cleaning. Existing sand pans are rectangular with uniform teeth along the sides of the pans. Thus blowdown flow draws fluid into the pan, but widely varying velocities exist and most of the blowdown is drawn from the teeth closest to the blowdown nozzle. The low velocity points will plug much faster than higher velocity points. Partially plugged sand pans are ineffective in removing solids in the regions beyond the plugged sections. Eventually the blow down flow will only flush small portions of the lower surface of the vessel near the blowdown nozzle.
Further, after the known flushing sequence, slurry remains within the sand pan. Solids settle from this slurry resulting in eventual plugging inside the sand pan.
It is desirable to have a sand pan and jet arrangement which is less prone to plugging than the prior art sand pans. This would permit longer runs between shutdowns for cleaning and/or less frequently blowing down the accumulated slurry.
It is therefore an object of the present invention to provide a sand pan which is less prone to plugging than prior art sand pans. In another aspect, it is an object to provide a process to remove settled solids from a fluid containment device that results in improved removal of solids.